[SI-LIST] Re: Amplitude loss ?
- From: Aubrey K Sparkman <asparky@xxxxxxxxxxxxxxxxxxxxxxxx>
- To: steve weir <weirsi@xxxxxxxxxx>, rajneesh shukla <rajneeshs123@xxxxxxxxx>
- Date: Fri, 06 Jan 2012 07:50:28 -0600
Rajneesh,
I think the issue is that you have not considered the relationship between
rise time and data rate.
Eric Bogatin wrote an article on "when loss matters". Essentially, when
the data rate is slow with respect to the rise time or said another way,
when the signal makes it to a one or zero and stays there for some time
before another transition, then loss doesn¹t matter. This is also when
when ISI is negligible. For this case dielectric loss doesn't matter and
it takes a VERY long, narrow trace for the Ohmic loss to matter.
On the other hand, what has been discussed below is when ISI is very
significant and data rate is fast with respect to rise time. In this
scenario, the transition will get only 50% to 70% (perhaps even loss for
very high data rates or long traces) of the way from Vmax to Vmin or back
before another transition starts. It this case both ohmic (series) and
dielectric (shunt) loss matter. Dielectric loss gets more discussion
because it it the dominant loss factor.
Does this help?
Aubrey Sparkman
SparkRight Solutions
On 1/6/12 7:05 AM, "steve weir" <weirsi@xxxxxxxxxx> wrote:
>For an electrically long, matched transmission line, the source is
>isolated from distant loads, including shunt losses. The source does
>not pump more power into the line as we increase those losses. Less
>power reaches the far end. Because we stipulated a matched channel, the
>far end impedance is unchanged. Less power at a constant real impedance
>translates to less voltage.
>Steve.
>On 1/6/2012 4:45 AM, rajneesh shukla wrote:
>> Steve,
>>
>> There is a law of conservation of energy but no law for conservation
>> of voltage and If we use ohm's law, voltage drop(loss) occurs only
>> when there is series impedance in load path.
>> As per ohm law, there won't be any voltage drop if we connect shunt
>> impedance to load. *I am all confused because I am not seeing any
>> series impedance in transmission line( when conductor loss is zero) so
>> where my voltage is dropping ?*
>> Agree that when ever there is a change in impedance there will be
>> change in energy dissipation or i should say change in energy
>> reflection or absorption but *my concern here is amplitude of signal
>> which is voltage( Energy per unit charge) not total energy.* In free
>> coffee example, I agree you can't make free cofee as there will be
>> energy loss due to dielectric loss*but why you think dielectric energy
>> loss mean voltage loss ? *
>> **
>> Rajneesh
>> On Fri, Jan 6, 2012 at 5:04 PM, steve weir <weirsi@xxxxxxxxxx
>> <mailto:weirsi@xxxxxxxxxx>> wrote:
>>
>> Dielectric loss does not increase the effective impedance of
>> either the near-end or far-end ports.
>>
>> Steve.
>>
>>
>> On 1/6/2012 3:14 AM, rajneesh shukla wrote:
>>>
>>> Thanks Steve but question remains unanswered !!
>>>
>>> I agree there will be a loss in energy due to dielectric loss but
>>> I was talking about loss in amplitude of signal (voltage) not
>>> loss in total energy, Energy loss does not always translates into
>>> voltage loss, right ? Receiver senses voltage( Potential Energy
>>> per unit charge) not total energy.
>>>
>>> As per basic circuit theory, If I have a driver that has zero o/p
>>> impedance is driving a 50 Ohm load and now if I connect 100 Ohm
>>> resistance across this load, Though there is energy loss due to
>>> 100 ohm resistance but still my load will see the same voltage,
>>> agree ?
>>>
>> No I do not agree. If you change the port impedance you will
>> change the amount of energy absorbed and the amount of energy
>> reflected.
>>
>>
>>> In transmission line, If series loss i.e. conductor loss is zero
>>> then I don't find the reason of any voltage drop in transmission
>>> line coz dielectric loss which is shunt loss can only dissipate
>>> total energy but can't change amplitude(voltage) of signal.
>>>
>> No I do not agree. If such a thing were true then you could heat
>> your coffee for free by making a long transmission line and
>> setting your cup on top of it.
>>
>>> Do you find any discrepancy in this analogy ?
>>>
>> Yes: Conservation of Energy and Ohm's Law.
>>
>>>
>>>
>>> On Fri, Jan 6, 2012 at 2:40 PM, steve weir <weirsi@xxxxxxxxxx
>>> <mailto:weirsi@xxxxxxxxxx>> wrote:
>>>
>>> Follow the energy. Achieve enlightenment. Of the energy
>>> that a shunt
>>> draws, how much of that energy remains available to the signal?
>>>
>>> Steve.
>>> On 1/6/2012 12:54 AM, rajneesh shukla wrote:
>>> > Experts,
>>> > As we know for perfectly matched line insertion loss is due
>>> to ohmic&
>>> > dielctric losses and due to these losses we see loss in
>>> rise/fall time as
>>> > well as loss in amplitude of signal.
>>> >
>>> > My question is what actually affects amplitude loss, is it
>>> ohmic loss or
>>> > dielectric loss ? My understanding says, it should be ohmic
>>> loss as
>>> > it comes in series coz dielectric one is shunt loss. If
>>> this analogy is
>>> > correct then a channel having very low ohmic loss but
>>> significant
>>> > dielectric loss will have only changes in rise time but
>>> minimal amplitude
>>> > loss, right ??
>>> >
>>> > Rajneesh
>>> >
>>> >
>>> >
>>>
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>>
>>
>> --
>> Steve Weir
>> IPBLOX, LLC
>> 150 N. Center St. #211
>> Reno, NV 89501
>> www.ipblox.com <http://www.ipblox.com/>
>>
>> (775) 299-4236 Business
>> (866) 675-4630 Toll-free
>> (707) 780-1951 Fax
>>
>> All contents Copyright (c)2012 IPBLOX, LLC. All Rights Reserved.
>> This e-mail may contain confidential material.
>> If you are not the intended recipient, please destroy all records
>> and notify the sender.
>>
>>
>
>
>--
>Steve Weir
>IPBLOX, LLC
>150 N. Center St. #211
>Reno, NV 89501
>www.ipblox.com
>
>(775) 299-4236 Business
>(866) 675-4630 Toll-free
>(707) 780-1951 Fax
>
>All contents Copyright (c)2012 IPBLOX, LLC. All Rights Reserved.
>This e-mail may contain confidential material.
>If you are not the intended recipient, please destroy all records
>and notify the sender.
>
>
>
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